System and Method for Using a PHY to Locate a Thermal Signature in a Cable Plant for Diagnostic, Enhanced, and Higher Power Applications

ABSTRACT

A system and method for using a physical layer device to locate a thermal signature in a cable plant for diagnostic, enhanced, and higher power applications. Cable heating in specific sections of a network cable is detected through an automatic identification of a thermal signature in electrical measurements of a network cable. The correlation of the thermal signature to a specific section of the network cable enables network personnel to locate hot spots in the network cable with ease.

This application is a divisional of non-provisional application Ser. No.11/761,419, filed Jun. 12, 2007, which is incorporated by referenceherein, in its entirety, for all purposes.

BACKGROUND

1. Field of the Invention

The present invention relates generally to network cabling systems andmethods and, more particularly, to a system and method for using aphysical layer device (PHY) to locate a thermal signature in a cableplant for diagnostic and higher power applications.

2. Introduction

Heat can have a significant impact on the performance of a networkcable. One problem that heat presents is the reduced cable operationalparametrics for data transmission. In one example, heat can affect theinsertion loss of the cable, thereby impacting data transmission on thecable. More generally, heat can affect the lifetime of the cable and itsconstituent materials and components.

While the general temperature of the entire cable can present an issue,the creation of a hot spot on a cable can also present significantissues. Hot spots on the cable can occur at localized points due to theconstricted dissipation of heat caused by physical constraints such asconduits, poor air circulation, etc. Hot spots can be of concern becauseof the creation of dangerous heat conditions near other activeequipment. Additionally, these hot spots can affect the data integrityin neighboring cables. As these examples illustrate, identifying theexistence of hot spots in the network infrastructure can be ofsignificant interest to IT personnel that are tasked with managing adata network infrastructure.

Additionally, hot spots are of significant interest to power overEthernet (PoE) networks, which provide power to remote devices overnetwork cables. The IEEE 802.3af and 802.3at PoE specifications providea framework for delivery of power from power sourcing equipment (PSE) toa powered device (PD) over Ethernet cabling. In these applications, hotspots can produce reduced cable operational parametrics for powertransmission. For example, heat will affect the resistance of the cable,which in turn will have an impact on the power transmission.

Locating hot spots in a network infrastructure is important for data andpower transmission network operations. Conventional diagnostictechniques are typically focused on measuring the overall thermalcondition of the entire length of cable. What is needed therefore is amechanism that enables a diagnosis of the cabling infrastructure toidentify the existence and location of hot spots in the network cables.

SUMMARY

A system and/or method for using a PHY to locate a thermal signature ina cable plant for diagnostic, enhanced, and higher power applications,substantially as shown in and/or described in connection with at leastone of the figures, as set forth more completely in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered limiting of its scope, the invention will be describedand explained with additional specificity and detail through the use ofthe accompanying drawings in which:

FIG. 1 illustrates an embodiment of a Power over Ethernet (PoE) system.

FIG. 2 illustrates a flowchart of a cable diagnostic process.

FIGS. 3A and 3B illustrate an example of an effect of localized heatingon cable measurements.

FIG. 4 illustrates an embodiment of a PoE environment at a PSE thatenables a cable monitoring process.

FIG. 5 illustrates an embodiment of a PoE environment at a PD thatenables a cable monitoring process.

FIG. 6 illustrates a flowchart of a cable monitoring process.

DETAILED DESCRIPTION

Various embodiments of the invention are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the invention.

FIG. 1 illustrates an embodiment of a power over Ethernet (PoE) system.As illustrated, the PoE system includes power sourcing equipment (PSE)120 that transmits power to powered device (PD) 140. Power delivered bythe PSE to the PD is provided through the application of a voltageacross the center taps of transformers that are coupled to a transmit(TX) pair and a receive (RX) pair of wires carried within an Ethernetcable. The two TX and RX pairs enable data communication betweenEthernet PHYs 110 and 130.

As is further illustrated in FIG. 1, PD 140 includes PoE module 142. PoEmodule 142 includes the electronics that would enable PD 140 tocommunicate with PSE 120 in accordance with a PoE standard such as IEEE802.3af, 802.3at, etc. PD 140 also includes pulse width modulation (PWM)DC:DC controller 144 that controls power FET 146, which in turn providesconstant power to load 150. As would be appreciated, FET 146 couldoptionally be integrated with PWM controller 144.

In standard PoE system (e.g., IEEE 802.3af and legacy systems), eachwire conductor has a specified current limit of 175 mA, resulting in atotal specified current limit of 350 mA. In PoE+ system (e.g., IEEE802.3at, its variations, and higher power proprietary schemes), higherper conductor current limits would be specified. The net effect of thepassage of such levels of current through the wire conductor is thegeneration of heat. This heat can have a significant impact on theoperation of the PoE system.

In higher power PoE+ applications, the first order constraint on howmuch current can be carried by the cabling system is the amount of heatthe system experiences. This results because the heat has a directeffect on safety and the long-term life expectancy of the cable itself.Additionally, excess heat can also lead to the degradation of the datatransmission capabilities of the cable. Because cabling systems are invery diverse environments, the heating effects can come from a varietyof sources: heat generated within the cable itself, the environmenttemperature, the restriction in airflow in the environment (likeconduits), neighboring cabling, etc.

As noted, the bundling of cables can create significant heat issues. Forexample, it is not uncommon to see massive bundles of cables (e.g.,90-150) leaving a data center or wiring closet. Moreover, conduits thatmay be within environmental constraints experience very limited airflow,thereby exacerbating the high temperature impact.

One of the concerns in PoE and PoE+ systems is the impact of havingspecific segments of the cable be exposed to higher temperatures thanthe remainder of the cable. For example, it is not uncommon to have along cable routed through poorly cooled conduits in the building walls,run along an air conditioning system, or near the roof of a building ina hot external environment. Cable routings that experience one or moreof these situations can lead to hot spots that are difficult to detectusing discrete temperature readings taken at selected points of thecable. In general, these discrete temperature readings seek to discernthe general temperature of the cable, not the existence of variations inthe temperature of different segment of the cable.

It is therefore a feature of the present invention that a diagnosis toolis provided that can automatically locate temperature variances along alength of a cable. The location of these temperature variances wouldenable an IT professional to diagnose the cabling plant quickly toidentify potentially hot sections of the cable. This automated diagnosiswould save significant time and expense as compared to the manualinspection of a length of cable. Significantly, once a hot section ofthe cable is identified, the situation can be rectified, or the cablecan be removed from use.

To illustrate the general process of the present invention, reference ismade to the flowchart of FIG. 2. As illustrated, the diagnostic processbegins at step 202, where one or more electrical characteristics of acable are measured. At step 204, it is determined whether the measuredelectrical characteristics include a thermal signature indicative of athermal discontinuity in a section of the cable. Here, the thermalsignature would appear as an effect generated by a type of discontinuityin the cable due to the increased heat in that cable section. In asense, the thermal signature would be similar to that produced by adiscontinuity such as a connector, only the discontinuity would not beas abrupt but more evenly spaced out.

In one embodiment, the diagnostic process can use the electricalmeasurements attributable to different sections of the cable as a proxyfor the variance in temperature between those different sections. Forexample, the electrical measurements at the end of the cable and at thesection of interest can yield a variance in temperature between the endof the cable and the hotspot. In various embodiments, this process canbe performed in correlation with a local temperature measurement atequipment such as that at an end of a cable, performed using acalibration mechanism, or performed based on a measured profile.

In one embodiment, the electrical measurements are passed to a CPU for adetermination of the location of the hot spot via correlation of theelectrical measurement to a length down the cable. In anotherembodiment, the electrical measurements are passed to the CPU forprocessing as a proxy for temperature measurements.

If it is determined at step 204 that a thermal signature has not beenidentified, then the process would end or would loop back to step 202for further measurements. If, on the other hand, it is determined atstep 204 that a thermal signature has been identified, then the processwould proceed to step 206, where a diagnostic report would be prepared.In one example, the diagnostic report would indicate the particularsection or point in a cable that contains the thermal discontinuity. ITprofessionals could then check the cable condition at that cable sectionor point to determine whether a thermal issues exists. This automateddiagnostic tool would obviate the need for the IT professional toperform an end-to-end inspection of the cable.

In one embodiment, a PHY is configured to identify the hot spot usingelectrical measurements that span an entire length of a cable. Oneexample of such an electrical measurement is a time domain reflectometry(TDR) measurement, which directly measures reflections. FIGS. 3A and 3Billustrate an example of the effect of a hot spot on an electricalmeasurement. As illustrated in FIG. 3B, a localized heating conditioncan produce a mid-span reflection that is measured by PHY1. The locationor cable section of the hot spot is determined through the measureddiscontinuity. In another example, the location of the hot spot can beidentified through the monitoring of the taps of an echo canceller. APHY typically cancels echo along the entire length of the cable. As aresult, echo cancellers can have taps that cover the entire length ofthe round-trip delay of the channel. These taps would enable the PHY toadapt to changes in the channel. Here, the PHY would analyze the echotaps to determine whether a temperature signature indicative of a hotspot is present. As the echo taps can be directly related to thedistance along the cable, the exact section of the cable where the hotspot exists can be identified. Regardless of the mechanism foridentifying the hot spot, the location information can be used by an ITtechnician to address the temperature issue quickly.

In one embodiment, the electrical measurements taken by the PHY for afirst section of the cable can be compared to electrical measurementstaken for other sections of the cable (e.g., adjacent sections) toidentify a temperature discontinuity. In another embodiment, theelectrical measurements taken by the PHY are compared to previouselectrical measurements to track the change over time. In this relativeanalysis, the differential change in the electrical measurements can becorrelated to the increased heat at a particular section of the cable.

As would be appreciated, the principles of the present invention are notdependent on the particular electrical measurement that is performed bythe PHY. Any electrical measurement that changes based on a change intemperature, and that can be correlated to a section of the cable can beused.

For example, a PHY can use a crosstalk measurement to identify atemperature signature. As the temperature of the cable changes, thecross talk measurement also changes. Here, the cross talk response curvecould change with temperature (e.g., changes in the magnitude of theresponse, shape of the curve envelope, etc.). Analyzing the responsecurve or monitoring the changes over time can then be correlated to atemperature change in a particular section of the cable. A disadvantageof using crosstalk measurements is that PHYs typically cancel crosstalkin the first 20-30 m of the cable. As such, full coverage of the entirelength of cable by a PHY on one end may not be practical. In accordancewith the present invention, the temperature signature analysis can beperformed on either side or on both sides of the cable. Where theparticular temperature signature analysis by a PHY may be distancelimited, the temperature signature analysis can be performed on bothends of the cable to achieve a more complete diagnostic over the entirecable length.

FIG. 4 illustrates an embodiment of a PoE environment 400 at a PSElocation in which the principles of the present invention can beimplemented as part of a monitoring scheme. As illustrated, environment400 includes PHYs 416-1 to 416-N that are each connected to Ethernetswitch 414. While a PHY can include one or more Ethernet transceivers,the wiring for only a single transceiver is illustrated as beingconnected to PHY 416-N. As would be appreciated, a PHY can be discreteor integrated as part of Ethernet switch 414. Each PHY is also connectedto CPU 412, although only a single connection from CPU 412 to PHY 416-Nis shown for simplicity. In one embodiment, CPU 412 is incorporatedalong with Ethernet switch 414 and PHYs 416-1 to 416-N on a single chip410. In another embodiment, Ethernet switch 414 and PHYs 416-1 to 416-Nare incorporated on a single chip separate from CPU 412, whereincommunication with CPU 412 is enabled via a serial interface. Alsoillustrated in PoE environment 400 is a PSE 420 that provides powerthrough the center taps of the transformers shown. As illustrated, PSE420 is also coupled to CPU 412 via opto-isolator 430 that facilitates anisolation boundary.

As noted, the electrical measurements could also be taken by theEthernet transceiver at the PD location. FIG. 5 illustrates anembodiment of a PoE environment 500 at a PD location. As illustrated,environment 500 includes PHY 516 that is connected to Ethernet switch514. As would be appreciated, the PHY at the PD can include one or moreEthernet transceivers. PHY 516 is also connected to CPU 512. In theillustrated embodiment, CPU 512 is incorporated along with Ethernetswitch 514 and PHY 516 on a single chip 510. In another embodiment,Ethernet switch 514 and PHY 516 are incorporated on a single chipseparate from CPU 512, wherein communication with CPU 412 is enabled viaa serial interface. Also illustrated in PoE environment 500 is PD 520that extracts power from the center taps of the transformers shown. Asillustrated, PD 420 is also coupled to CPU 512 via opto-isolator 530that facilitates an isolation boundary.

As noted, measurements can be taken at the PSE and/or at the PD. If bothends of the link have the measurement capability, then the measurementdata or analysis results can be exchanged between the PSE and the PD asrequired. A benefit of a dual monitoring capability is the increasedaccuracy of using two sources of information and/or analysis. In variousembodiments, communication between the PD and the PSE can occur via aLayer 1 scheme, such as voltage and/or current modulation, Layer 2(packets), Layer 3 (packets) or any such combination. Packets may be astandard protocol such as Ethernet, LLDP, OAM, or a proprietary systemover these protocols.

To illustrate the operation of a PoE environment in implementing amonitoring scheme of the present invention, reference is now made to theflowchart of FIG. 6. As illustrated, the flowchart of FIG. 6 begins atstep 602 where a transceiver in a PHY measures electricalcharacteristics of an Ethernet cable coupled to the PHY. In oneembodiment, these electrical measurements are taken during an echocanceller convergence process performed by an echo canceller moduleunder control of the CPU. Electrical measurements taken by thetransceiver are then transmitted to the CPU at step 604. As noted, themeasurements or results from a first end of a link can be transmittedremotely to the other end of the link. For example, the measurementstaken at a PD can be transmitted to a PSE for analysis.

At step 606, the electrical measurements are then analyzed. In oneembodiment, the electrical measurements can be analyzed either alone orin comparison with prior measurements. In another embodiment, theelectrical measurements can be analyzed with reference to knownmeasurements/temperatures and/or profiles.

Regardless of the particular methodology of analysis, at step 608, it isthen determined whether a temperature signature has been detected. If nochange is detected at step 608, then the process would loop back wherefurther measurements are taken by the Ethernet transceiver. In thisperiodic monitoring process, the delay between measurements can beimplementation dependent. For example, the delay between measurementscan range from fractions of a second to tens of seconds or more. Here,the determined delay can be chosen to provide the system operator withany desired granularity of monitoring.

If a temperature signature is detected at step 608, then an impact onthe PoE system configuration and/or operation is determined at step 610.In one embodiment, the PoE system can first change the allowable maximumpower/current for that link. This maximum can be a new maximum that isdetermined independent of a power demand/budget, average cabletemperature, cable capacity, etc. The new maximum can then be comparedto the current power transmission as well as incoming requests. If themaximum is exceeded, then a change in the power applied by the PoEsystem over that cable is made with a notification to the entire system(PD and PSE). In general, the potential impact could consider a changein operation of a single PoE channel, or a group of PoE channels. Aswould be appreciated, the particular impact of an identified temperaturesignature on a cable can vary depending on the application.

One of the benefits of the present invention is that the temperaturemonitoring does not rely on probes at different points in the cable. Notonly would the setting up of probes be impractical and not economicallyfeasible, but the monitoring based on these probe measurements wouldalso not be sufficient to guarantee that there isn't a problem on aparticular section of the cable. For example, the cable may have a hotspot in a section of the cable that lies within a hot conduit.

Finally, it should be noted that the principles of the present inventioncan be applied to any form of network cabling, whether standard Ethernetcabling (e.g., Category 3, 5, 5e, 6, 7, etc.), non-standard cabling suchas Type-II cabling, shielded, or unshielded cabling. Also, theprinciples of the present invention can be applied to PoE systems thatuse two pairs as well as four pairs. For four-pair systems, theindividual pairs can be analyzed independently or as a system.

These and other aspects of the present invention will become apparent tothose skilled in the art by a review of the preceding detaileddescription. Although a number of salient features of the presentinvention have been described above, the invention is capable of otherembodiments and of being practiced and carried out in various ways thatwould be apparent to one of ordinary skill in the art after reading thedisclosed invention, therefore the above description should not beconsidered to be exclusive of these other embodiments. Also, it is to beunderstood that the phraseology and terminology employed herein are forthe purposes of description and should not be regarded as limiting.

1. A power over Ethernet system for identifying a location of atemperature hot spot on an Ethernet cable, comprising: a powered devicedetection component that detects a presence of a powered device, saidpowered device coupled to a power sourcing equipment port via anEthernet cable; and a power controller that controls power allocation tosaid power source equipment port based on electrical measurements ofsaid Ethernet cable taken by a physical layer device, said electricalmeasurements being correlated to a temperature signature indicative of atemperature hotspot in a subsection of said Ethernet cable.
 2. The powerover Ethernet system of claim 1, wherein said electrical measurementsare taken periodically by said physical layer device.
 3. The power overEthernet system of claim 1, wherein said electrical measurements aretaken by said physical layer device during an echo cancellation process.4. The power source equipment of claim 1, wherein said electricalmeasurements includes echo return loss.
 5. The power source equipment ofclaim 1, wherein said electrical measurements includes time domainreflectometry.
 6. The power source equipment of claim 1, wherein saidelectrical measurements includes cross talk.
 7. The power sourceequipment of claim 1, wherein said power controller controls an aspectof operation of said power sourcing equipment based on said indicationof said temperature hotspot.
 8. The power source equipment of claim 7,wherein said aspect of operation is a change in current threshold atsaid power sourcing equipment.
 9. The power source equipment of claim 7,wherein said aspect of operation is a change in power consumption atsaid powered device.
 10. A cable diagnostic system that identifies atemperature hot spot in a network cable, comprising: a physical layerdevice that measures an electrical characteristic of a network cablethat provides an operable data transmission path between a first deviceand a second device; a controller that determines whether an analysis ofsaid measured electrical characteristic indicates an existence of atemperature signature, said controller also being configured to generatea report based on said determination, said report including a locationalong said network cable at which a temperature hot spot is suspected.11. The cable diagnostic system of claim 10, wherein said physical layerdevice measures said electrical characteristic during an echocancellation process.
 12. The cable diagnostic system of claim 10,wherein said controller is part of a power over Ethernet system.
 13. Thecable diagnostic system of claim 10, wherein said electricalcharacteristic is one of echo return loss or cross talk of said networkcable.
 14. The cable diagnostic system of claim 10, wherein saidphysical layer device is associated with a power sourcing equipment. 15.The cable diagnostic system of claim 10, wherein said physical layerdevice is associated with a powered device.